Heretofore, an extruded foam employing a polypropylene resin has been known. For example, although a high expansion ratio is usually difficult to achieve by a polypropylene resin, Patent Document 1 describes an extruded polypropylene type resin foam having a high expansion ratio of at least 10 times, an average cell size of as small as less than 400 μm and a closed cell ratio of at least 40%, which is obtained by employing a polypropylene resin having an excellent viscoelastic property that is obtained by adjusting the molecular weight and the molecular weight distribution. By this process, since it is possible to produce an extruded foam having many cell walls, it is possible to efficiently shield radiation heat from the outside according to the document.    Patent Document 1: WO2006/054714